Geared flywheel?

[SnakeEye]

I have lately been trying to google up some information about geared flywheels, and come up with very little. This is the short list of what I know:

Gearing a flywheel to run at a higher speed than the crankshaft has a dramatic influence on the relationship of energy stored vs. moment of inertia. The energy stored in a flywheel is proportional to the flywheel's moment of inertia multiplied by the square of the rotational speed. Thus, gearing the flywheel to run at 2x crank speed would require 1/4 the moment of inertia, at 3x crank speed 1/9 the moment of inertia, etc.

Running a geared flywheel puts extreme loads on the flywheel drive system, much higher than the load absorbed by the PTO. Any simple way of arranging such a drive (such as a heavy duty chain drive) puts serious radial loads on the crankshaft. The fact that the load changes direction twice per combustion cycle means that there is very little room for drive system flex, making chain drives even more complicated (the chain would have to be extremely tight, and heavy enough that chain stretch does not become a factor). A planetary gear arrangement would avoid this, but is complicated enough to make the idea slightly unpalatable.

The above mentioned complications have prevented geared flywheels from becoming a commonly used technology, thus making it more difficult for an amateur to experiment with them, as information on the subject is not easily accessible. However, using diesel engines in motorcycles does pose some unique challenges, and a ways to reduce flywheel mass and diameter have been discussed over and over again. Perhaps the advantages of reduced weight and height (for dry sump engines) are important enough to warrant the added complication?

Does anyone know where I can find more information about this?

Thoughts?

[XLerate]

I can't envision the flywheel system or any part of it, whether direct drive off of crankshaft or gear/chain driven, 'reversing direction' on any engine. The pistons, valves and pushrods reverse direction, not crank and flywheel.

Also if you're going to talk about inertial mass working to advantage then it doesn't help to reduce that mass by lightening the flywheel does it?

Overall the simpler a system or design is the less possibility of complicated problems showing up.

[Blunt Eversmoke]

It's quite clear that weight savings are possible with geared flywheels; however, doing it right implies eliminating side load on the shafts in question - and deeply integrating the flywheel either into the engine (possibly the best way, but, sadly, not done to date) or into the transmission.

[XLerate]

I'll have trouble explaining myself here, but that never stopped me before

A lot of this centers around the simple question of what it is you want: horsepower or torque?

For a hot, high horsepower engine we have to spin up everything inside into the higher rpm's, where horsepower is produced, as quickly as possible. For a gasser this horsepower threshold occurs at about 5,200 rpm, not sure on diesel. That means we want lightened flywheel, lightened connecting rods, lighter pistons and anything else we can do to get the mass spinning as fast as possible and as soon as possible, for QUICK rpms.

Diesel engine's most desireable characteristic is the fantastic torque that's produced at very low rpm, almost full torque right off idle or by 1,200-1,300 rpms and onto about 3,500 rpm. For this type of power curve all those lighter components aren't desireable and will even defeat the major plus factor for diesels: MONSTER TORQUE!

Yes, there's always been those who are trying to get the best of both worlds out of diesels, to hopefully keep the massive torque beyond 3,500 rpm but also spin it up quicker and higher and fuel it into high rpm horsepower. The idea is to merge the two power curves to keep it building or at least holding torque until the horsepower really starts kicking in at higher rpms, without a gap in between and without scattering parts in all directions. It's quite a challenge. 8,000 rpms and diesel aren't something said in the same breath.

The second major plus feature of diesels sort of comes with the territory. Because it's built for huge torque at low rpms the mass of heavy duty parts, their pure brute strength, plus low rpm power means a very durable and long lasting engine, far beyond gassers by as much as 5 times the accumulated mileage between rebuild$!

Seeing these two features together, tremendous torque and incredible durability, in many cases the quest for high horsepower diesels, quckly spinning up lightweight parts to 5,000+ rpms, is self defeating. I'm prejudiced there and it's just my take on the issue, not saying I'm right...

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[Stuart]

Would running a lighter flywheel at higher speeds exhibit the same gyroscopic effect as a slower, heavier flywheel? Probably, I'm thinking, so no noticable affect on handling?
On a similar (gyroscopic) note, leaning a old fashioneddiesel bike over left or right can have a terminal effect on fuel supply as it acts on the internal components on the guvnor. But I digress..

[Rhynri]

I can't envision the flywheel system or any part of it, whether direct drive off of crankshaft or gear/chain driven, 'reversing direction' on any engine. The pistons, valves and pushrods reverse direction, not crank and flywheel.

I think he's referring to the load on the flywheel system, from being driven by the piston to driving the piston (The power stroke vs the unpowered stroke), one set imparts energy to the system the others remove it.

Or at least that's how I read it. But i'm on new seizure meds, so hey.

[tappy]

My thinking on this is that the stationary engine's (from welders etc) that are being used on here, have very heavy flywheels for several reasons.

One is to reduce the acceleration of the engine. If it's hooked up to a generator, spinning at 3600rpm and the power demand suddenly disappears (welder is switched off) then a heavy flywheel gives the fuel governer a chance of responding and reducing the fuelling before the engine revs itself into the stratosphere.

The second is that the flywheels are often used as fans, made in cast iron (cheap) and no-one minds if the engine weighs an extra few kilos.

The third is that the injection timing is static, set for best power and /or economy at 3000rpm. This means they're probably running a bit too advanced at idle, so a nice heavy flywheel helps smooth tickover and starting.

To improve the dynamic performance of these engines (increase acceleration, reduce gyroscopic effects) it seems likely that a flywheel with less inertia can probably be used, but you might want to raise tickover slightly, use a decompressor for starting, need alternative methods of providing cooling air, and - ideally - use variable injection timing.

[XLerate]

I can't envision the flywheel system or any part of it, whether direct drive off of crankshaft or gear/chain driven, 'reversing direction' on any engine. The pistons, valves and pushrods reverse direction, not crank and flywheel.

I think he's referring to the load on the flywheel system, from being driven by the piston to driving the piston (The power stroke vs the unpowered stroke), one set imparts energy to the system the others remove it.

Or at least that's how I read it. But i'm on new seizure meds, so hey.

Bummer on the seizure stuff, sorry to hear that! I found by accident that oxygen therapy, pure oxygen off a bottle or semi-pure off a concentrator, cuts seizures from 20-30 minutes to 3-5 minutes! Doesn't apparently prevent them but helps some and when they do hit it's over real quick. Oxygen may help prevent the more severe effects while they're ocurring too.

[Rhynri]

They are Petit Mal (Absence) Seizures so it could be worse, still makes a mess out of your day sometimes, I have them quite frequently and they like erasing the parts of my day directly before they occur, which is what first alerted me to them. It could be worse though.